The present invention relates to a medical device for placing an embolic coil at a preselected location within a vessel of the human body, and more particularly, relates to a flexible delivery member having a heating element and a polymer tether member at the distal tip of the delivery member for holding the embolic coil in order to transport the coil to a desired position within the vessel and release the embolic coil at that position.
For many years flexible catheters have been used to place various objects within the vessels of the human body. Such devices include dilatation balloons, radiopaque markers, liquid medications and various types of occlusion devices such as balloons and embolic coils. Occlusion devices including embolic coils can be used to treat aneurysms or to occlude the blood vessel at a target location.
Coils which are placed in vessels may take the form of helically wound coils, or alternatively, may be randomly wound coils, convoluted coils, coils wound within other coils or many other such configurations to better occlude a blood vessel. Embolic coils are generally formed of radiopaque biocompatible metallic materials, such as platinum, gold, tungsten, or alloys of these metals. The coils can be coated with various materials to improve thrombogenicity. Often times, several coils are placed at a given location in order to occlude the flow of blood through the vessel by promoting thrombus formation at the particular location. The decreased blood flow reduces the pressure on the aneurysm and reduces the risk of a ruptured.
In the past, embolic coils have been placed within the distal end of the catheter. When the distal end of the catheter is properly positioned the coil may then be pushed out of the end of the catheter with, for example, a guidewire to release the coil at the desired location. This procedure of placement of the embolic coil is conducted under fluoroscopic visualization such that the movement of the coil through the vasculature of the body may be monitored and the coil may be placed at the desired location. With these placements systems there is very little control over the exact placement of the coil since the coil may be ejected to a position some distance beyond the end of the catheter.
Patients with potentially life-threatening hemorrhagic brain aneurysms are in need of a safe, reliable, accurate, and fast release mechanism for the deposition of embolic coils via catheters. Numerous procedures have been developed to enable more accurate positioning of coils within a vessel. One commercial product of current use is the Guglielmi Detachable Coil (GDC). The GDC utilizes the electrolytical dissolution of a designated guidewire junction to generate the release action. This procedure typically takes 10-30 minutes and is difficult to control in a reliable fashion. The effects of the dissolved material in the blood stream create a potential hazard to the patient. Problems that have been associated with the release of the coil include the force of the coil exiting the delivery catheter causing the coil to overshoot the desired site or dislodge previously deployed coils. Thus, even with the numerous prior efforts to develop miniature actuators for catheter-based therapeutic application, there remains a need for safe, fast release actuator mechanisms for the delivery of embolic coils, for example.
Another problem with embolic coil delivery systems that rely on a stiff pusher wire extending through the entire length of the catheter to push an element out of the distal end of the catheter is that the pusher wire inherently causes the catheter to be very stiff with the result that it is very difficult to guide the catheter through the vasculature of the body. Accordingly, there is a need for a mechanism for deploying embolic coils from the distal end of a catheter having a flexible body.
There is also a need for precise therapeutic actuators configured to deploy therapeutic elements or devices, e.g. embolic coils, within the narrow confines of blood vessels in the human brain, e.g. 250-500 micrometers in diameter. The present invention satisfies these and other needs.